Image processing used for skin assessment, such as for measurement of an allergic or skin reaction during standard Skin Prick Testing, is hampered by a number of variables that are often not well controlled and can even be inconsistent within a typical medical dermatology or allergy practice. Specific variables that can affect measurement accuracy include the following:
Lighting conditions: Ambient light can vary due to variables such as type of fluorescent or incandescent light source used, illumination angle, and collimation of light illuminating the subject's arm or back, to name a few.
Visual acuity and skill of nurse or other practitioner: Depending on the visual acuity and judgment of the practitioner administering the allergy test or performing other skin imaging, measurement variability can result even under well-controlled lighting conditions. Even among well-trained professionals, the resulting measurement is ultimately subjective due to differences in criteria and judgment for wheal/flare visibility.
Irregularity and asymmetry of reactions: Wheal features, geometries, and dimensions, including pseudopodia and other irregular skin reactions can vary from one patient to the next. Such irregularity complicates quantification of reaction extent.
Differences in patient skin tone and overall skin condition: Skin color, differences in overall melanin content, aging, and other factors complicate the task of achieving a consistent basis for measurement, including measurements of change in reaction over time.
As is well known to those who study the subject in detail, human skin is itself highly variable from one person to the next and exhibits significant differences even over different areas of the same person. The task of making accurate measurements of features on the skin surface is highly complex when compared with making comparable measurements of relatively homogeneous surfaces. The complexity of this task is particularly appreciated by practitioners who test skin response for determining allergic sensitivity. Current test methods that analyze test results using the human eye can be cumbersome, inaccurate, and time-consuming, as well as uncomfortable for the patient. The accuracy of current manual test methods is disappointing. There is a significant chance of error due to the complicated nature of the steps involved in executing the test sequence and analyzing results. Coupled with these problems is the overall difficulty of getting patients into an office for testing, particularly for elderly or pediatric patients, and for underserved patient populations.
Current skin prick testing for allergic reaction requires using extensive amounts of the skin surface area. For example, the conventional skin prick test for 24 different allergens requires use of both arms of a typical patient, with as much as 1 or more inches between each skin prick site. Improvements for more efficient testing have been proposed, such as the skin test device described in U.S. Pat. No. 5,099,857 entitled “Medical Testing Device with Calibrated Indicia” to Baldo et al. (Baldo '857) that packages a number of capsules and needles for allergen testing in a single patch. Baldo '857 states that a minimum distance between capsule/needle units should be about 20 mm, so that a 4×6 test patch array with 24 skin prick sites would require an area of the skin of at least about 80×120=9600 mm2.
Conventional testing methods are disclosed in a reference paper relating to image processing on wheals: “Automatic Measurement of Skin Wheals Provoked by Skin Prick Tests”, Stud. Health Technol. Infor. 2005, Vol 116, pp 441-446 by M. Prinz, K. Vigl, and S. Wohrl. In this case, wheals are identified, and their outlines marked on a separate sheet for transfer to a computer scan able medium. The process requires manual identification and outlining of the wheal dimensions. It is time-consuming and is prone to the same human measurement errors as the standard skin prick test. It is impractical to use this method for small wheal diameter measurement.
There is a need to have a means to interpret and analyze skin response data in a consistent and straightforward manner that provides improved accuracy over existing methods. What is desired is an easy and consistent methodology to automatically analyze the image data obtained by allergy testing.